Can and could exercises

http://www.englishexercises.org/makeagame/viewgame.asp?id=7710

http://www.englishexercises.org/makeagame/viewgame.asp?id=3826

http://www.agendaweb.org/verbs/modals-can-could-exercises.html

http://www.esl-lounge.com/student/grammar/1g101-elementary-can-could-gap-fill-exercise.php

http://www.englishclub.com/grammar/verbs-modals_can_quiz.htm